The long-term goal of this research is to understand the molecular action and resistance mechanisms of two important classes of insecticides, pyrethroids and sodium channel blocker insecticides (SCBIs). Strategies for the control of arthropod pests of major public health concerns continue to rely heavily on the use of relatively safe insecticides. Currently, pyrethroids are the only class of insecticides used in insecticide treated nets (ITNs) for malaria control, due to their fast acting, high efficacy, and relative low toxicity to humans. However, a major threat to the sustained use of pyrethroids is the development of resistance. Indoxacarb and its active metabolite (DCJW), the first member of a new class of SCBIs, also meets vector control criteria, and could be an alternative insecticide to pyrethroids. Both pyrethroids and indoxacarb target voltage-gated sodium channels; however, the modes of their action are not well understood at the molecular level, which presents a major obstacle to the characterization of mechanisms of resistance. The specific aims of this renewal proposal are: 1) Characterization of the molecular basis of pyrethroid action and resistance, and 2) Identification of the receptor site and molecular action of indoxacarb/DCJW on sodium channels. A combination of molecular, electrophysiological, and computer modeling methods will be used to test novel hypotheses, with the final goal of defining the molecular identities of the elusive pyrethroid and indoxacarb receptor sites on the insect sodium channel. New knowledge gained from this fundamental research will have significant impact on future development of effective monitoring and management strategies for controlling major human health-threatening arthropod pests.